Field of the Invention
The invention relates to novel benzidine derivatives (benzidine=4,4'-diaminobiphenyl), to a process for their preparation, and to their use as hole transport materials in organic light emitting diodes (OLEDs).
Hole-transport materials based on tetraarylbenzidine are described, for example, in the dissertation by J. Simmerer "Ladungstransport in kolumnaren Phasen" [Charge transport in columnar phases], Bayreuth 1996, (pages 4 to 10); in this connection, see also: "Molecular Crystals and Liquid Crystals", Vol. 183 (1990), pages 217 to 226, "Applied Physics Letters", Vol. 65 (1994), pages 807 to 809, and "Chemical Physics", Vol. 200 (1995), pages 245 to 255.
The materials disclosed hitherto absorb and emit exclusively in the UV region of the electromagnetic spectrum.